A061860 Variant of A061417.

1, 2, 4, 11, 28, 152, 726, 5268, 40438, 365944, 3628810, 39974466, 479001612, 6228256404, 87178339984, 1307706805928, 20922789888016, 355688409760972, 6402373705728018, 121645133931170028, 2432902008232456692

Offset

0,2

Comments

Does this count some variety of necklaces?

Links

G. C. Greubel, Table of n, a(n) for n = 0..445

Formula

a(n) = (1/n)*Sum_{d|n} phi(n/d)*C(n, d)*(d!).

Maple

[seq(A061860(j), j=1..40)]; with(numtheory); A061860 := proc(n) local d, s; s := 0; for d in divisors(n) do s := s + phi(n/d)*(binomial(n, d))*(d!); od; RETURN(s/n); end;

Mathematica

a[n_] := DivisorSum[n, EulerPhi[n/#] Binomial[n, #] (#!)&]/n; Array[a, 25] (* Jean-François Alcover, Mar 06 2016 *)

Crossrefs

A061860[p] = A061417[p] = (p-1)!+(p-1) for all prime p's.

Sequence in context: A005503 A148139 A336871 * A093960 A267912 A118311

Adjacent sequences: A061857 A061858 A061859 * A061861 A061862 A061863

Keyword

nonn

Author

Antti Karttunen, May 11 2001

Status

approved